Wang Yi, Baiutti Federico, Gregori Giuliano, Cristiani Georg, Salzberger Ute, Logvenov Gennady, Maier Joachim, van Aken Peter A
Max Planck Institute for Solid State Research , Heisenbergstrasse 1, 70569 Stuttgart, Germany.
ACS Appl Mater Interfaces. 2016 Mar;8(10):6763-9. doi: 10.1021/acsami.5b12813. Epub 2016 Mar 7.
Using spherical aberration corrected high-resolution and analytical scanning transmission electron microscopy, we have quantitatively studied the lattice distortion and the redistribution of charges in two-dimensionally strontium (Sr)-doped La2CuO4 superlattices, in which single LaO planes are periodically replaced by SrO planes. As shown previously, such structures show Tc up to 35 K as a consequence of local charge accumulation on both sides of the nominal SrO planes position. This is caused by two distinct mechanisms of doping: heterogeneous doping at the downward side of the interface (space-charge effect) and "classical" homogeneous doping at the upward side. The comparative chemical and atomic-structural analyses reveal an interrelation between local CuO6 octahedron distortions, hole spatial distribution, and chemical composition. In particular we observe an anomalous expansion of the apical oxygen-oxygen distance in the heterogeneously doped (space-charge) region, and a substantial shrinkage of the apical oxygen-oxygen distance in the homogeneously doped region. Such findings are interpreted in terms of different Jahn-Teller effects occurring at the two interface sides (downward and upward).
利用球差校正的高分辨率分析型扫描透射电子显微镜，我们定量研究了二维锶（Sr）掺杂的La₂CuO₄超晶格中的晶格畸变和电荷重新分布，其中单个LaO平面被SrO平面周期性取代。如前所示，由于在名义SrO平面位置两侧的局部电荷积累，此类结构显示出高达35 K的转变温度（Tc）。这是由两种不同的掺杂机制引起的：界面下方的非均匀掺杂（空间电荷效应）和界面上方的“经典”均匀掺杂。对比化学和原子结构分析揭示了局部CuO₆八面体畸变、空穴空间分布和化学成分之间的相互关系。特别是，我们观察到在非均匀掺杂（空间电荷）区域中，顶端氧-氧距离出现异常增大，而在均匀掺杂区域中，顶端氧-氧距离大幅缩小。这些发现是根据在界面两侧（下方和上方）发生的不同 Jahn-Teller 效应来解释的。
